The Avengers series and Civil War has been on a decline. Infinity War while I think will open bigger than the three will be the most frontloaded like they tend to be and do something like $210M/$450M.
I don't think Vaughn is directing a hypothetical Superman 2. I don't think it'll happen for a while, I can see Superman taking a Hulk/Black Widow like role for a while, having big appearances in other movies like Shazam and Flashpoint.